Field of the Invention
This invention generally relates to opto-mechanical devices for producing images to be displayed and more specifically to opto-mechanical devices for use in procedures requiring miniaturized imaging devices.
Description of Related Art
In recent years endoscopic and other like imaging systems have been developed to display an image on a video monitor. These imaging systems typically include opto-mechanical devices with housings for supporting optical devices such as objectives of one or more lenses. An objective forms an image for being conveyed to a remote video processor. In some applications, an image sensor proximate the objective interfaces with the objective and converts the incoming light from the objective into digital signals that are coupled to a video processor. Other applications define an interface for one end of a coherent fiber bundle and an objective; the other end of the bundle terminates with a remote connection to the video processor. In either embodiment glass objectives are preferred for good image quality.
Customers for such devices, particularly in the medical field, also express a desire for imaging systems with minimal cross-sections, particularly systems that can be manufactured at low cost and in high volumes for single-use, disposable instrumentation. Recently imaging sensors have become available with cross-sections of less than 2 mm. and with pixel densities that provide good image resolution. However, prior art optical devices have not been available for interfacing with such image sensors in commercially acceptable production quantities and costs.
As known, the production of a larger, conventional lens involves grinding and polishing end surfaces of an optical glass blank to form two polished spherical optical surfaces spaced along an axis. Each lens then undergoes edge grinding to reduce the lens diameter to a specified value and to align the optical and mechanical axes. United States Letters U.S. Pat. No. 7,715,105 (2010) to Forkey et al. for an Acylindrical Optical Device discloses an alternative by which small diameter lenses are manufactured from over-sized lens elements and other optical elements formed into lens systems. Edges are sawn into each lens system to reduce its overall size. Sawing can be applied to integral lens elements or lens arrays. As an alternative, lenses also can be molded from glass or plastic. Photolithographic techniques constitute another alternative that can be used to fabricate lenses on a wafer, such as included in an image sensor.
Prior art molding processes become difficult to implement for the production of small lenses with diameters less than 2 mm. It is difficult to obtain acceptable resolution with plastic lenses of this size. Edge grinding, such as used with manufacture of standard lenses, must be undertaken with tighter controls for increased accuracy. Edge grinding is also time-consuming and therefore increases manufacturing costs. The above mentioned sawing process may not be appropriate for newer applications, particularly those which require high-volume, low cost production. Lithographic processes can be applied only to a limited number of materials and have limited radii of curvature. Consequently they are unlikely to provide a lens with a high index of refraction and/or short radius of curvature as is required for obtaining a large field of view with small lenses.
What is needed is an opto-mechanical assembly constructed with a diameter of in the order of 2 mm or less that can interface with a small image sensor or coherent fiber bundle wherein the opto-mechanical assembly can be provided in sufficiently large volumes and at sufficiently low costs such that instruments incorporating such assemblies can be made as disposable instruments or components thereof.